The invention relates to a system and method to operate an internal combustion engine to facilitate the operation of secondary devices, such as emission aftertreatment devices, which depend on the operating condition of the engine to which they are coupled. In the present invention, the internal combustion engine is part of a hybrid vehicle system.
The primary function of an automobile is to transport passengers and cargo. There are, however, secondary vehicular functions including cooling the vehicle cabin, heating the vehicle cabin, and exhaust aftertreatment functions to lower the emission of regulated gaseous components from the vehicle which are performed as well. In a conventional vehicle, the operating condition of the engine must be selected to provide the torque demanded by the operator. The secondary functions are typically attended to by operating the engine at a condition which provides the desired power but may be less than a desirable operating condition from the standpoint of providing the best function of the engine dependent auxiliary device, i.e., the device which provides the secondary function. Several examples of the problems encountered in providing secondary functions in conventional vehicles follow.
If the temperature in a vehicle cabin increases above a set point of an air-conditioner thermostat, engine power is increased to provide power to drive the air conditioning compressor, while maintaining desired power at the wheels, i.e., the primary function. Increasing the power level of the engine is inefficient at many operating conditions. Clearly, it would not be satisfactory to the operator of the vehicle to delay air conditioning until the engine happened to be at a desirable condition to facilitate efficient employment of the air conditioner. Thus, in a conventional vehicle, the engine power is raised and a large fuel penalty may result.
A diesel engine equipped with a diesel particulate filter requires periodic regeneration of the filter to avoid complete occlusion of the filter. There are engine operating conditions which could cause the carbonaceous material collected in the filter to spontaneously ignite and oxidize. However, the filter must be regenerated at the time that it has become full, regardless of the current engine operating condition. Prior art approaches include electrically heating the particulate filter to the auto ignition temperature of the particulate matter, providing a burner in the exhaust system to ignite the particulate matter, operating the engine at a retarded injection timing or with exhaust gas recirculation (EGR) to cause the exhaust temperature to rise, and others. However, all prior art methods penalize fuel efficiency and many of them do not guarantee regeneration success over all possible operating scenarios.
A further example of a problem in operating a secondary device occurs in diesel-equipped conventional vehicles in which cabin heating is notably slow. Measures may be undertaken to promote cabin warm up. However, these measures negatively impact fuel economy and are insufficient to provide the desired cabin comfort to the operator. Thus, heating of the cabin may be delayed until an engine operating condition is accessed which can satisfy both the primary function, i.e., power at the driving wheels, and the secondary function, heating the cabin.
Yet another example of a challenge in providing a secondary function in a vehicle is in managing lean NOx traps (LNTs) for exhaust aftertreatment of homogeneous charge (fuel and air premixed) and stratified charge (fuel and air separated) lean burn engine exhaust. LNTs collect NOx during lean operation o f the engine and subsequently release and react the NOx during a period of rich operation. One of the difficulties encountered in conventional vehicles utilizing an LNT is in maintaining smooth torque in making transitions between lean and rich operation to purge the LNT of NOx.
The inventors of the present invention have recognized a method to operate a hybrid vehicle system, i.e., one with an internal combustion engine and another machine which may provide motive force to the wheels, in such a manner to satisfy or attend to demands of engine dependent auxiliary devices to better provide secondary functions, such as emission control, cabin heating, and cabin cooling.
A hybrid vehicle system including at least two machines capable of being coupled to and capable of providing motive force to the vehicle""s driving wheels is provided. One of the machines is an internal combustion engine. The system includes one or more engine dependent auxiliary devices which are coupled to the internal combustion engine. An engine controller determines whether a current engine operating condition satisfies an engine dependent auxiliary device and if the engine dependent auxiliary device is not satisfied, the engine controller determines a desired engine operating condition to satisfy the engine dependent auxiliary device. The engine dependent auxiliary device may be a lean NOx trap, a lean NOx catalyst, a particulate filter, a fuel vapor purge system, a compressor of an air conditioning unit, and a heat exchanger for transferring heat to a cabin of the vehicle.
A method to manage an internal combustion engine within a hybrid vehicle system is disclosed. The vehicle system includes at least two machines capable of being coupled to and capable of providing motive force to the vehicle""s driving wheels; one of which is an internal combustion engine. In the method, whether the current engine operating condition satisfies the needs of an engine dependent auxiliary device is determined. If the engine dependent auxiliary device is not satisfied, a desired engine operating condition, which satisfies the engine dependent auxiliary device, is determined and the engine is caused to attain the desired engine operating condition.
An advantage of the present invention is that by operating the engine at its most efficient operating condition while providing a secondary function, such as cabin cooling, the fuel penalty exacted by providing that secondary function is minimized. This is possible because the internal combustion engine, which is installed in a hybrid vehicle system, need not be constrained to develop torque which matches the power demanded by the driver.
A further advantage of the present invention is that torque fluctuations of the engine to provide transitions, for the purposes of a secondary device, may be made without affecting torque at the driving wheels. The process of making transitions is greatly simplified because engine torque need not be constant; the second machine of the hybrid system may absorb excess torque or provide makeup torque desired at the driving wheels. Furthermore, transitions may take place in a more fuel efficient manner than provided in prior art. Examples are transitions between lean and rich conditions to purge a LNT, transitions to and from an operating condition which causes auto ignition of a diesel particulate filter, and transitions between stratified lean and stratified homogeneous operation in a stratified charge engine.
Still a further advantage of the present invention is that secondary functions can be provided upon demand rather than having to postpone providing the function or inadequately providing the function. Examples include heating the cabin of a vehicle equipped with a diesel engine and regenerating a diesel particulate filter, both of which may suffer significant delay in prior art methods.
Yet a further advantage of the present invention is that it may be possible to attend to two secondary devices simultaneously. As an example, vapor purge and LNT purge might be concurrently provided by accessing an engine operating condition which satisfies both.